Systems and Methods for Performing Carrier Aggregation Based on Subframe Configuration

1. A method for performing carrier aggregation based on subframe configuration, the method comprising: determining that conditions for a wireless device in communication with an access node meet a carrier aggregation criteria, wherein the access node and wireless device communicate using a first subframe configuration; receiving signal information from the wireless device comprising received signal levels for a plurality of candidate secondary carriers; retrieving subframe configurations used by the candidate secondary carriers to communicate with wireless devices; selecting one or more of the plurality of candidate secondary carriers based on the received signal level information and the retrieved subframe configurations; and activating carrier aggregation such that the one or more selected secondary carriers are used to transmit downlink data to the wireless device.

2. The method of claim 1 , wherein selecting one or more of the plurality of candidate secondary carriers further comprises: determining a number of downlink subframes for each of the retrieved subframe configurations; and selecting one or more of the plurality of candidate secondary carriers based on the received signal level information and the number of downlink subframes for the retrieved subframe configurations.

3. The method of claim 2 , wherein selecting one or more of the plurality of candidate secondary carriers further comprises: comparing the received signal levels for the plurality of candidate secondary carriers to a criteria; and selecting one or more of the plurality of candidate secondary carriers based on the comparison between the received signal levels and the criteria and the number of downlink subframes for the retrieved subframe configurations.

4. The method of claim 2 , wherein selecting one or more of the plurality of candidate secondary carriers further comprises: determining a signal level criteria for each of the candidate secondary carriers based on the retrieved subframe configuration for the candidate secondary carrier; comparing the received signal levels for the plurality of candidate secondary carriers to the determined criteria for each candidate secondary carrier; and selecting one or more of the plurality of candidate secondary carriers based on the comparison between the received signal levels and the criteria and the number of downlink subframes for the retrieved subframe configurations.

5. The method of claim 4 , wherein the signal level criteria for a particular candidate secondary carrier is determined based on a number of downlink subframes for the retrieved subframe configuration corresponding to the particular candidate secondary carrier.

6. The method of claim 2 , wherein selecting one or more of the plurality of candidate secondary carriers further comprises: comparing downlink subframe slots for the retrieved subframe configurations with uplink subframe slots for the first subframe configuration, wherein the comparing identifies retrieved subframe configurations that have a slotted downlink subframe that conflicts with a slotted uplink subframe for the first subframe configuration; and selecting one or more of the plurality of candidate secondary carriers based on the received signal level information, the number of downlink subframes for the retrieved subframe configurations, and the identified conflicts.

7. The method of claim 2 , wherein selecting one or more of the plurality of candidate secondary carriers further comprises: selecting a first of the plurality of candidate secondary carriers based on the received signal level information and the retrieved subframe configurations; determining whether to select a second candidate secondary carrier based on a number of downlink subframes for the subframe configuration corresponding to the first candidate secondary carrier; and selecting a second candidate secondary carrier based on the received signal level information and the retrieved subframe configurations when it is determined that a second candidate secondary carrier should be selected.

8. The method of claim 7 , further comprising determining to select a second candidate secondary carrier when the number of downlink subframes for the subframe configuration corresponding to the selected first candidate secondary carrier fails to meet a criteria.

9. A method of claim 1 , wherein at least one of the candidate secondary carriers is transmitted from a second access node and retrieving the subframe configuration for the at least one of the candidate secondary carriers comprises receiving the subframe configuration over an X2 communication link connecting the access node and the second access node.

10. A system for performing carrier aggregation based on subframe configuration, the system comprising: an processing node with a processor configured to: determine that conditions for a wireless device in communication with an access node meet a carrier aggregation criteria, wherein the access node and wireless device communicate using a first subframe configuration; receive signal information from the wireless device comprising received signal levels for a plurality of candidate secondary carriers; retrieve subframe configurations used by the candidate secondary carriers to communicate with wireless devices; select one or more of the plurality of candidate secondary carriers based on the received signal level information and the retrieved subframe configurations; and activate carrier aggregation such that the one or more selected secondary carriers are used to transmit downlink data to the wireless device.

11. The system of claim 10 , wherein selecting one or more of the plurality of candidate secondary carriers further comprises: determining a number of downlink subframes for each of the retrieved subframe configurations; and selecting one or more of the plurality of candidate secondary carriers based on the received signal level information and the number of downlink subframes for the retrieved subframe configurations.

12. The system of claim 11 , wherein selecting one or more of the plurality of candidate secondary carriers further comprises: comparing the received signal levels for the plurality of candidate secondary carriers to a criteria; and selecting one or more of the plurality of candidate secondary carriers based on the comparison between the received signal levels and the criteria and the number of downlink subframes for the retrieved subframe configurations.

13. The system of claim 11 , wherein selecting one or more of the plurality of candidate secondary carriers further comprises: determining a signal level criteria for each of the candidate secondary carriers based on the retrieved subframe configuration for the candidate secondary carrier; comparing the received signal levels for the plurality of candidate secondary carriers to the determined criteria for each candidate secondary carrier; and selecting one or more of the plurality of candidate secondary carriers based on the comparison between the received signal levels and the criteria and the number of downlink subframes for the retrieved subframe configurations.

14. The system of claim 13 , wherein the signal level criteria for a particular candidate secondary carrier is determined based on a number of downlink subframes for the retrieved subframe configuration corresponding to the particular candidate secondary carrier.

15. The system of claim 11 , wherein selecting one or more of the plurality of candidate secondary carriers further comprises: comparing downlink subframe slots for the retrieved subframe configurations with uplink subframe slots for the first subframe configuration, wherein the comparing identifies retrieved subframe configurations that have a slotted downlink subframe that conflicts with a slotted uplink subframe for the first subframe configuration; and selecting one or more of the plurality of candidate secondary carriers based on the received signal level information, the number of downlink subframes for the retrieved subframe configurations, and the identified conflicts.

16. The system of claim 11 , wherein selecting one or more of the plurality of candidate secondary carriers further comprises: selecting a first of the plurality of candidate secondary carriers based on the received signal level information and the retrieved subframe configurations; determining whether to select a second candidate secondary carrier based on a number of downlink subframes for the subframe configuration corresponding to the first candidate secondary carrier; and selecting a second candidate secondary carrier based on the received signal level information and the retrieved subframe configurations when it is determined that a second candidate secondary carrier should be selected.

17. The system of claim 16 , where the processing node is further configured to determine to select a second candidate secondary carrier when the number of downlink subframes for the subframe configuration corresponding to the selected first candidate secondary carrier fails to meet a criteria.

18. A system of claim 10 , wherein at least one of the candidate secondary carriers is transmitted from a second access node and retrieving the subframe configuration for the at least one of the candidate secondary carriers comprises receiving the subframe configuration over an X2 communication link connecting the access node and the second access node.